(Adds new polls, quote from former prosecutor general Rodrigo Janot)
By Anthony Boadle and Brad Brooks
BRASILIA/SAO PAULO, Oct 27 (Reuters) - The chances of Brazil's leftist presidential candidate Fernando Haddad narrowing the lead of right-wing front-runner Jair Bolsonaro took a hit when he failed to win a crucial endorsement on Saturday, a day before the two face off in a runoff election.
However, polls published late Saturday from Brazil's two biggest surveying firms showed momentum shifting toward Haddad, though he still trails Bolsonaro by a solid margin.
Former center-left candidate Ciro Gomes said in a video on social media that he would not take sides in the election campaign, withholding support for Haddad of the Workers Party (PT).
Gomes, a former governor of Ceará state in the northeast, is influential in Brazil's poorest region. His endorsement could have given Haddad a big lift in the South American country's most polarized election in a generation.
But Rodrigo Janot, Brazil's influential former prosecutor general under whose watch the country's unprecedented investigations and prosecutions of endemic political graft took place, tweeted late Saturday that he would vote for Haddad. That was a blow to Bolsonaro's work positioning himself as the only anti-corruption candidate.
"I think we are at the brink of a process that could push our democracy beyond its limits," Janot told Reuters late Saturday. "Freedom, equality and fraternity - always and at any cost."
MOMENTUM IN POLLS
Haddad narrowed Bolsonaro's lead to 8 percentage points in an Ibope poll released late Saturday, a survey that gave him 46 percent compared with Bolsonaro's 54 percent.
As only two candidates remain and those figures discard voters who say they will annul their votes, that in practice means Haddad needs to win 5 percentage points to overtake the right-winger.
In a Datafolha poll also released late Saturday, Bolsonaro had 55 percent of voter backing, compared with 45 percent for Haddad.
While Haddad failed to get Gomes to endorse him, he won the backing on Saturday not just of Janot but of Brazil's most popular YouTube host, Felipe Neto, who has 27.7 million followers on his channel. A popular anti-corruption judge, Joaquim Barbosa, who jailed several top PT leaders for corruption, also came out for Haddad.
Gomes finished third in the Oct. 7 first round vote with 12 percent of the vote, behind Bolsonaro's 46 percent and Haddad's 29 percent. Gomes had hoped to be the standard bearer of the left but was outmaneuvered by jailed PT leader Luiz Inacio Lula da Silva, who is serving a 12-year prison sentence for corruption and anointed Haddad as his stand-in.